On Tue, Jun 26, 2018 at 10:21 PM Juan Nunez-Iglesias <jni.s...@gmail.com> wrote:
> Let me start by thanking Robert for articulating my viewpoints far better > than I could have done myself. I want to explicitly flag the following > statements for endorsement: > > *I would still reserve warnings and deprecation for the cases where the > current behavior gives us something that no one wants. Those are the real > traps that people need to be warned away from.* > > > *In the post-NEP .oindex/.vindex order, everyone can get the behavior that > they want. Your argument for deprecation is now just about what the default > is, the semantics that get pride of place with the shortest spelling. I am > sympathetic to the feeling like you wish you had a time machine to go fix a > design with your new insight. But it seems to me that just changing which > semantics are the default has relatively attenuated value while breaking > compatibility for a fundamental feature of numpy has significant costs. > Just introducing .oindex is the bulk of the value of this NEP. Everything > else is window dressing.* > > > *If someone is mixing slices and integer indices, that's a really good > sign that they thought indexing behaved in a different way (e.g. orthogonal > indexing).* > > > I would offer the exception of trailing slices to this statement, though: > > In [1]: from skimage import data > In [2]: astro = data.astronaut() > In [3]: astro.shape > Out[3]: (512, 512, 3) > > In [4]: rr, cc = np.array([1, 3, 3, 3]), np.array([1, 8, 9, 10]) > In [5]: astro[rr, cc].shape > Out[5]: (4, 3) > > In [6]: astro[rr, cc, :].shape > Out[6]: (4, 3) > > This does exactly what I would expect. > Yup, sorry, I didn't mean those. I meant when there is an explicit slice in between index arrays. (And maybe when index arrays follow slices; I'll need to think more on that.) > Going back to the motivation for the NEP, I think this bit, emphasis mine, > is crucial: > > the existing rules for advanced indexing with multiple array indices are > typically confusing to both new, **and in many cases even old,** users of > NumPy > > > I think it is ok for advanced indexing to be accessible to advanced users. > I remember that it took me quite a while to grok NumPy advanced indexing, > but once I did I just loved it. > > I also like that this syntax translates perfectly from integer indices to > float coordinates in `ndimage.map_coordinates`. > > *I'll go on record as saying that array-likes should respond to `a[rr, > cc]`, as in Juan's example, with the current behavior. And if they don't, > they don't deserve to be operated on by skimage functions.* > > > (I don't think of us highly enough to use the word "deserve", but I would > say that we would hesitate to support arrays that don't use this > convention.) > Ahem, yes, I was being provocative in a moment of weakness. May the array-like authors forgive me. -- Robert Kern
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